1. Field of the Invention
The present invention relates to a display apparatus arranged to adjust the display state of an image displayed on an image plane in a display mode in which the setting values of brightness, contrast, contour enhancement, etc., for the image plane are combined.
2. Description of Related Art
Display apparatuses called head-mounted display apparatuses arranged to be used by mounting them on the heads of users (hereinafter referred to as HMDs) have been known. Many of the known HMDs are arranged to permit manual adjustment of the brightness of their image planes. The brightness of the image planes has been thus arranged to be set and adjusted to a desired brightness irrespective of the brightness of external environment of them.
However, the conventional HMDs have presented a problem which has required some improvement. When an HMD is used in a place such as a bright outdoor environment, particularly in a place receiving sunlight or under a bright illumination light, the external light enters the HMD through a gap between the HMD and the face of the user, as shown in FIG. 1. If the quantity of light from outside is larger than the light of a display image plane of the HMD, the image plane becomes difficult to see even with the image plane set brighter. In the case of liquid crystal display (LCD) image planes which are used in many HMDs, in particular, the increase of only the brightness of the image plane nullifies image contrast to whiten the whole image plane. Then, the HMDs become almost useless in such a state.
To solve this problem, some of HMDs have been developed to prevent external light from entering the eyes of the user, by providing some shield between the HMD and the face of the user. However, the use of the shield makes the HMD heavier and becomes a nuisance to the user as it covers all parts around the eyes. The use of such an HMD sometimes causes the user to feel oppressively warm or uneasy as it prevents the user from knowing the conditions of surroundings.